Snape: Good or Bad?

OK, the release of the 7th book of the Harry Potter series is on the horizon. So, here is your opportunity to answer that age-old question:

Is Severus Snape friend or foe?

The wife is utterly convinced that Snape is a good dude. She works in a local dental office, and it appears that no human under the age of 18 agrees with her. What do you think? Do you think that Snape is an unwilling aid to Harry’s cause? Or do you think that the Dark Lord controls Snape and he will eventually use weak little Severus to torment Harry?